Dopamine receptors mediate a number of central nervous system functions. Screening of clinical entities useful in the treatment of psychotic-like states revealed that many of the so-called "atypical" antipsychotics, which are characterized by reduced or absent extrapyramidal side effects (J. A. Lowe III, et al., Med. Res. Rev., 8, 475 (1988); M. Lader, J. Internat. Med. Res., 17, 1 (1989)), exhibit high binding affinities for the dopamine D.sub.4 receptor, especially as compared to the D.sub.2 receptor (Sokaloff, et al., Biochem. Pharmacol., 43, 659 (1992); Leysen, et al., Psycho-pharmacology, 112, S40-S54 (1993)). Seeman et al (Nature, 365, 441 (1993)) found that dopamine D.sub.4 receptors are elevated 6-fold in postmortem schizophrenic brain tissue. Several other studies using positron emission tomography (Farde, et al., Arch. Gen. Psychiatry, 47, 213 (1990); Wong, et al., Science, 234, 1558 (1986) also were interpreted to indicate an increase in dopamine D.sub.4 receptor levels in schizophrenics (Lahti, et al., Eur. J. Pharmacol., 236, 483 (1993)). These results support the usefulness of selective, high affinity dopamine D.sub.4 antagonists for the treatment, with reduced side effects, of psychotic-like diseases (Science, 265, 1034 (1994)). See also Meth. Find. Exp. Clin. Pharmacol. 16(5): 303-307 (1994), which discloses the receptor pharmacology of a human D.sub.4 -dopamine receptor expressed in HEK 293 cells from a synthetic gene, which receptor should be useful for the discovery and study of novel dopamine antagonists and agonist ligands.